近30年海南岛土壤有机质时空变异特征及成因分析
Scientia Agricultura Sinica（2019）
Abstract
[目的]土壤有机质(SOM)是评价土壤肥力和土壤碳库的重要指标.由于复杂的成土过程及人类活动的影响,SOM通常存在较强的时空变异性.研究SOM的时空变异特征可为农业种植结构调整、应对全球气候变化提供重要参考依据.[方法]以海南岛为研究区域,通过资料收集、野外调查、采样与分析获取全国第二次土壤普查(1980s)和2 01 2年0-20 cm土层SOM含量数据,首先采用随机森林模型分别对两个时期训练集41 0个、1 28个样点SOM空间分布规律进行预测,并通过验证集1 03个、32个验证点对模型精度进行验证;采用统计学方法,结合农业统计数据,研究时隔30年海南岛不同土地利用类型SOM时空变异特征,并对驱动因素进行探讨.[结果]1980s SOM含量均值为20.57 g·kg-1,呈现出从西南向东北降低的空间分布趋势,全岛SOM含量主要集中在15-20和20-30 g·kg-1两个等级,共占全岛面积的75.29％;2 01 2年SOM含量均值为15.89g·kg-1,呈现出西南和东北高,西部、南部沿海低的空间分布趋势,SOM含量主要集中在10-15和15-20 g·kg-1两个等级,共占全岛面积的78.28％,而15-20和20-30 g·kg-1两个等级占全岛面积66.04％,同1980s相比减少了9.25个百分点.[结论](1)时隔近30年,海南岛SOM含量整体呈减少趋势.2012年SOM平均含量较1980s减少了4.68 g·kg-1,减少率为22.75％.其中水田的SOM含量减少最为明显,减少了6.42 g·kg-1,减少率为27.34％;其次为园地,减少了2.65 g·kg-1,减少率为14.25％;而旱地减少量最小,为1.28 g·kg-1,减少率为8.84％;(2)水稻连作改为稻菜轮作(水田连作改为水旱轮作)、林地开垦为园地、土地利用强度加大是造成海南岛SOM含量下降的主要原因.
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